The development of vaccines to combat vaccine resistant cancers and infectious diseases has relied significantly on constructs employing subunit antigens. While the use of defined molecular antigens offers advantages in terms of safety and precision in immune response targeting, they are typically less immunogenic. Often, these vaccine formulations require an adjuvant, a substance that potentiates immune response. The critical roles of vaccine adjuvants lie in their ability to (1) enable the use of otherwise impotent antigens, (2) extend the benefits of vaccines to poor responders (e.g., older or immune-compromised patients), and (3) effect dose-sparing of rare and expensive antigens in short supply (e.g., in an epidemic). The natural product saponin QS-21 is the adjuvant of choice in numerous promising antitumor and antiviral vaccine clinical trials, despite liabilities associated with toxicity, chemical instability, and lack of availability in pure form. This grant application comprises a multi-disciplinary approach toward the chemical synthesis and immunological evaluation of several novel classes of newly discovered saponin adjuvants, including the jujubosides, lablabosides, and soyasaponins. The Specific Aims of this research program will involve: (1) the total synthesis of jujuboside A and analogs, employing a novel formal ketene-hetero-Diels-Alder reaction; (2) the semisynthesis of lablaboside F and analogs, employing a host of dehydrative, oxidative and imidate glycosylation methodologies developed in our laboratory; (3) the semisynthesis of soyasaponin A1 and analogs, employing novel variants of regio- and stereoselective 20 C-H activation with an aldoxime as the directing group; and (4) preclinical assessment of the synthetic saponin adjuvants, providing data for screening of adjuvant performance for future advancement to clinical trials. These efforts will address fundamental chemical and immunological questions associated with several novel promising saponin adjuvants, and holds the promise of yielding novel therapeutics in the vaccine arena.